Numerous strategies have been developed to assist vehicle operators during parking (e.g., reversing) maneuvers. Such vehicle park assist systems may include radar and/or ultrasonic emitters and sensors designed to alert the operator when object(s) are in vehicle's path. One or more visual and/or audio signals may alert the operator of an imminent collision so that appropriate countermeasures may be taken.
An example of a park assist system is a hybrid ultrasonic and radar backup aid disclosed in U.S. Pat. No. 5,754,123 issued to Nashif et al. on May 19, 1998. An apparatus according to the '123 patent includes ultrasonic sensors positioned at the rear of the vehicle providing continuous range information to a control module for objects that are detected as being relatively close to the vehicle. A radar system provides range information to the control module for objects detected beyond the range of the ultrasonic system. At low speeds below a predetermined minimum speed level or when the system is placed in the “park” mode for parking, the radar information is ignored and only the ultrasonic information is used to warn the vehicle operator. At a relatively high threshold backup speed, the vehicle operator is immediately warned to slow down, whether or not an object is detected in the vehicle path. Between the lower and upper threshold speeds, both the ultrasonic system and the radar system are used to continuously range and detect any objects that enter their respective detection fields. The control module causes an alarm device to warn the operator as to how close the vehicle is to the closest object.
Another example of a park assist system is one disclosed in U.S. Pat. No. 6,594,614 issued to Studt et al. on Jul. 15, 2003. A warning system according to the '614 patent scans behind the vehicle with an emitter/sensor system and determines a time-to-collision with the object based on distance to the object and vehicle speed. Based upon the time-to-collision, a simple combination of visual and audio signals is designed to let the operator known of the imminency of a collision with the object so that the operator may react and make appropriate countermeasures.
Other examples of vehicle park assist strategies include those disclosed by U.S. Pat. No. 6,446,998 issued to Koenig et al. on Sep. 10, 2002; U.S. Pat. No. 6,476,730 issued to Kakinami et al. on Nov. 5, 2002; and U.S. Pat. No. 5,754,123 issued to Adachi et al. on Aug. 28, 2001.
Although these and other strategies may provide effective assistance to vehicle operators during parking maneuvers, the use of attached vehicle trailers may interfere with the proper function of such warning systems. For example, a trailer attached to a rear portion of the vehicle may inappropriately and continuously activate visual and/or audio signals of an impending collision. To overcome this, vehicles may include a “switch” to deactivate the warning system. The use of a switch may increase the cost and complexity of the warning system and require the operator to manually de-activate and activate system. In some cases, the operator may de-activate the system and then forget to re-activate the system once the trailer is removed. What is needed, then, is a strategy for detecting the presence of a trailer thereby allowing for the automatic deactivation and activation of a park assist system.
Therefore, it would be desirable to provide a trailer detection circuit for a vehicle park assist system that overcomes the aforementioned and other disadvantages.